After the Origin

When the The Origin of Species was published,
Darwin carefully sent copies to all of the scientific leaders of
his day, both those he thought would hate the book and those he
hoped would love it. In all of his accompanying letters he was
extremely self-effacing. Darwin's old mentor, Adam Sedgwick, for
instance, wrote a savage review of Darwin's book in the Spectator.

His few supporters turned out to be those he had been
preparing all along: Hooker, Lyell, and, most importantly, Huxley.
Huxley, who up until this point had been supportive but never yet
entirely convinced, was finally firmly on Darwin's side after seeing
the abundant evidence and clear argumentation. Huxley was renowned
for his temper, and he soon became known as "Darwin's bulldog"
for his willingness to tenaciously defend the theory of evolution
by natural selection.

Huxley had a chance to test his teeth in a debate that
took place in 1860. Darwin's most vocal critics, aside from Sedgwick,
were the primate anatomist Richard Owen and the Bishop of Oxford,
Samuel Wilberforce. During the annual meeting of the British Association
at Oxford, after a talk that made some reference to Darwin's ideas,
Wilberforce gave a half-hour tirade against Darwinism. Huxley,
who was also in the audience, gave an impassioned reply, accusing
the Bishop of "prejudice and falsehood." Tensions were high. At the
time it was unclear who won the debate, but it has gone down in history
as victory for Darwin. In any case it was clear that Darwinism
could not be ignored.

Events like these made Darwin a household name, at least
among the well-educated and the well-off. He started receiving
visits from the literary and scientific stars of the day. But he
was still weak and prone to bouts of illness after too much socializing,
so during the next ten years he did his best to maintain his quiet,
isolated life at the Down House. He focused on some of the problems
that had fascinated him as a naturalist, turning away from the
theorizing that dominated his Origin of Species and
back to the close observation that had always satisfied him best.
Research for his books, On the Various Contrivances by
which Orchids are Fertilized by Insects and The
Movements and Habits of Climbing Plants, once again turned
his workshop and now his garden into a place of constant activity.
Unlike during his pigeon period, there was little carnage, except
when his interest briefly turned to insect-eating plants.

His most ambitious book during the 1860's was The
Variation of Animals and Plants under Domestication. Here
he tried to understand the dynamics of inheritance, the actual
mechanisms by which a pigeon with a slightly longer beak or oddly-colored
feather might pass its traits down to succeeding generations. He
correctly discovered that some traits tended to overpower others;
this corresponds to the modern concept of dominant and recessive
genes. But his "pan- genesis" theory of how traits were actually
passed from generation to generation was flawed. He thought that
each cell in the body contributed to the sperm and egg cells that
created new life. According to this theory, small particles called
gemules were supposed to travel from every cell of the body, through
the blood stream, to the sperm and eggs, thereby conveying information
about the current state of the organism. Part of the reason that
this theory appealed to Darwin was that it allowed changes that
occurred during an organism's lifetime to be inherited by the organism's
children: if the skin remained tan for long enough, the gemules
in those tanned skin cells would be transported to the egg or sperm
cells and thereby affect the skin color of future generations.
Unfortunately there was little evidence to support this theory,
even in the 1860's, and many of Darwin's peers, while admiring
his observations on variation, dismissed his theoretical explanation
of it.

After the Variations, Darwin's next big
project was to write a book on three topics: the evolution of the
human species, sexual selection, and the expression of emotions
in animals and humans. As usual, he had more to say on all three
of these topics than he originally thought, so the first two topics
were published in 1871's The Descent of Man, and Selection
in relation to Sex and the third topic a year later in
The Expression of Emotions in Animals and Man. Darwin
had never wanted to tackle the controversial issue of whether humans
were evolved just like other animals, hoping that some other well-
respected evolutionist would bite the bullet and write a definitive
defense of the idea. But when he realized that such a book was
not going to happen without him, he poured all of his enthusiasm
and obsession for detail into the project. The Expression
of Emotions itself, which has had an enormous impact on
the study of the physiology and psychology of emotion, can also
be read as a long argument on the unity of the human species with
its animal ancestors. Darwin expected outrage after publishing The Descent
of Man , but his expectations were disappointed. All of
the outrage had come twelve years earlier, when the Origin had
been published. Despite the care taken by Darwin in that earlier
work to avoid any mention of the human species, it was obvious
to many of the Origin's readers that all of the
arguments applied to pigeons could as well be applied to humans.
So by the time the Descent came out, when the Origin had
already been translated into German, Russian, Dutch, Italian, and
Swedish, the argument over the origin of the human species was
well-worn. Nevertheless the Descent provided a
powerful piece of ammunition in the continuing war between creationists
and evolutionists.